2014 Update on infectious disease

A total of 415 women received 30% oxygen and 416 were given 80% oxygen. The two groups were well matched for important confounding variables such as age, race, pari­ty, body mass index, number of prior cesarean deliveries, diabetes, cardiopulmonary disease, anemia, smoking, and chronic steroid use.

The groups did not differ in the frequency of surgical site infection or endometritis, which occurred at a rate of 2.4% in the group receiving 30% oxygen, compared with 2.9% in the group given 80% oxygen.

Rationale for oxygen supplementationAdequate tissue oxygenation has been observed to enhance the bactericidal function of neutrophils. So why were Duggal and colleagues unable to demonstrate a beneficial effect for oxygen therapy?

The most likely explanations:

• Their obstetric patients were less seriously ill than the general surgery patients undergoing colorectal surgery in the study by Greif and colleagues.
• Given the low overall rate of infection, their sample size may have been too small to show a statistically significant difference in outcome (Type II statistical error).

In point of fact, more than 80% of patients in both groups had scheduled cesarean deliveries, presumably prior to the onset of labor and ruptured membranes. The outcome may have been different had the groups included a majority of patients undergoing surgery after labor and ruptured membranes.

What this EVIDENCE means for practiceUntil additional studies are performed, I cannot recommend routine use of perioperative hyperoxygenation as a method of reducing the rate of surgical site infection and/or endometritis. However, we have very good scientific evidence indicating that the following measures significantly reduce the rate of endometritis after both scheduled and unscheduled cesarean delivery:
• administration of prophylactic antibiotics prior to the start of surgery
• removal of the placenta by gentle traction on the umbilical cord rather than by manual extraction.^3,4
Similarly, we have sound evidence demonstrating that the following measures significantly reduce the rate of surgical site infection:
• clipping, rather than shaving, the hair at the surgical site just prior to the incision
• preoperative cleansing of the surgical area with chlorhexidine
• administration of prophylactic antibiotics prior to the start of surgery closure of the lower half of the subcutaneous tissue (if it exceeds 2 cm in thickness) using a relatively noninflammatory suture such as polyglactin or polyglycolic acid.

The presence of E coli in a midstream urine specimen is highly predictive of UTI

Hooton TM, Roberts PL, Cox ME, Stapleton AE. Voided midstream urine culture and acute cystitis in premenopausal women. N Engl J Med. 2013;369(20):1883–1891.

Urinary tract infections (UTI) are among the most common infections experienced by women of all ages. Asymptomatic bacteriuria affects 5% to 10% of all sexually active women. During the course of their lifetime, at least 50% of women develop some form of UTI.

Pyelonephritis is not nearly as common as asymptomatic bacteriuria or cystitis, but this infection can be especially dangerous in older, debilitated women who reside in nursing homes and require indwelling catheters.

The most common organisms that cause UTIs in women are the aerobic gram-negative bacilli, principally Escherichia coli, Klebsiella species, and Proteus species. Other Gram-negative bacilli such as Pseudomonas species, Serratia, or Enterobacter are not common uropathogens except in immunosuppressed hosts or patients who have long-term indwelling catheters. Gram-positive organisms such as group B streptococci, enterococci, and staphylococcal species are occasional pathogens but, as Hooton and colleagues demonstrate in this study, perhaps not quite as important as we once thought.

Related articles:
• Update on infectious disease. Alan T. N. Tita, MD, PhD (June 2011)
• Have you tried these innovative alternatives to antibiotics for UTI prevention? Patrick A. Nosti, MD; Kate C. Arnold; Cheryl B. Iglesia, MD (February 2013)

Details of the studyUsing an elegantly simple design, the Hooton team studied women aged 18 to 49 years who had symptoms suggestive of acute cystitis. They collected two urine specimens from each woman for culture—one was collected using the midstream, clean-catch technique and the other by catheterization. They then compared microbial species and colony counts in the paired specimens to determine the positive and negative predictive values of midstream culture results, using the catheterized culture results as the reference standard.

The 226 women in the study experienced 236 clinical episodes suggestive of acute cystitis. One hundred forty-two (70%) of the catheterized specimens were positive for infection; of these, four specimens yielded more than one uropathogen. One hundred fifty-seven (78%) of the midstream specimens were positive for infection.

The presence of E coli in the midstream culture was highly predictive of a positive culture for E coli by catheterization, even when the cutoff was only 100 colonies/mL on the midstream specimen (positive predictive value, 93%). However, neither the presence of enterococci nor the presence of group B streptococci, at any colony count, was predictive of a positive culture by catheterization. Interestingly, among 41 patients who had either enterococci or group B streptococci in their midstream culture, E coli was present in the catheterizedculture in 61% of cases, suggesting that infection with E coli may be the more important cause of the patient’s symptoms.